In this worsening climate of great-power tension and mistrust, the nuclear arms-control regime long in place between the United States and Russia is in danger. And without it, efforts to stop the spread of nuclear weapons, or at least limit their role in international affairs, are also in trouble. For instance, the prospect of heading off a destabilizing nuclear-arms competition in Asia, including between China and the United States, will further recede, as will the appeal of the U.S.-Russian precedent of restraint for India and Pakistan. America and Russia remain overwhelmingly the world’s strongest nuclear-armed powers, and their example is crucial for the future of nonproliferation, disarmament and the global nuclear peace.

A key mechanism here is the historic 1987 intermediate range nuclear forces (INF) treaty, under which Moscow and Washington banned the deployment of a whole destabilizing class of nuclear-armed missiles. Despite signs that Russia had violated this agreement as far back as 2010, and concerns voiced by Putin in 2007 that China also ought to be included, only now have things come to a head. U.S. president Barack Obama recently took the extraordinary step of sending a letter to Vladimir Putin, levelling the accusation that Russia is in breach of its solemn treaty commitments by testing cruise missiles with a range between 500 and 5,500km since 2008.

Given the high state of current tensions, including fears of a Russian invasion of eastern Ukraine and international outrage over the shooting down of passenger flight MH17, it is difficult to imagine Russia and the United States now putting aside their differences to prioritize a reinvigoration of nuclear arms control.

But recent events aren’t the only threat to strategic arms control between the United States and Russia—for two reasons. First, existing treaties such as New START (2010) and the INF don’t address modern and nascent nuclear capabilities present in the U.S.-Russian relationship, such as sea-launched cruise missiles. And second, politically and strategically, there seems to be no great momentum, nor will in either camp to move forward on nuclear risk mitigation as there was during the abortive “reset” of Obama’s first presidential term. President Obama’s great hopes for a world without nuclear weapons, proclaimed in Prague in 2009, are more than ever confronted by ugly geopolitical realities.

Of course, the obvious benefit of nuclear arms control is that it reduces the numbers of these devastating weapons deployed for potential use. But equally important is the less-measurable benefit produced by a system of inspections, building confidence and providing strategic warning. Thus under New START, numbers of non-deployed weapons were proverbial low-hanging fruit traded in return for access and verification. In turn, Washington and Moscow established a practical, normative mechanism for crisis stability.

Nuclear weapons may quietly cast a long shadow over the current Ukraine crisis—their very existence must be considered a major restraint on a Western military response, and perhaps as a reminder of that, Russia has conducted drills simulating a NATO nuclear strike. Whatever else he fears, Putin is presumably concerned that were Ukraine to join NATO, it would become part of a nuclear-armed alliance able to deter Russia and, in theory, strike first in a crisis. It can also be argued that Russia’s renewed interest in previously-banned, intermediate-range missiles is partly a product of Russian concern about NATO capabilities, such as ballistic-missile defences, submarine-launched cruise missiles and progress on technology, such as hypersonic glide vehicles required to achieve the objectives of what is known as Prompt Global Strike. Russia’s argument, right or wrong, is that these undermine the deterrence stability established during the close of the Cold War.

For its part, Washington has not gone into depth about what is wrong with Russia’s violation of the treaty other than it puts European allies at risk and that it hopes it can negotiate a return to “compliance.” The United States sees its own actions as being in line with the stabilizing and reassuring objective of having a wide range of non-nuclear options for its treaty commitments in Europe and its capability to deter without having to resort to nuclear threats.